Force balance system



R. s. FLEMING ETAL 3,021,820

FORCE BALAN Feb. 20, 1962 CE SYSTEM Original Filed Feb. 18, 1959 uomaowmOmDOm umswwmmm INVENTORS ROBERT S.FLEM|NG y WARREN H. GOWLES RAYMONLENSING R [0 I ATTORNEYS United States Patent 3,021,820 FORCE BALANCESYSTEM Robert S. Fleming, Warren H. Cowles, and Raymond L.

Ensinger, Detroit, Mich, assignors to Holley Carburetor Company, Warren,Mich, a corporation of Michigan Original application Feb. 18, 1959, Ser.No. 794,016. Divided and this application Aug. 22, 19150, Ser. No.

12 Claims. (Cl. 12141) The invention relates to force balance systemsand refers more specifically to simplified apparatus for producing anoutput displacement proportional to an input force thereto which inputforce is a function of a variable external parameter.

This application is a division of our copending application, Serial No.794,016, filed February 18, 1959.

It is well known that parameters of speed, temperature and pressure areused independently and/or collectively for controlling and determiningthe operation of gas turbine power plants, and various hydraulicmechanisms have been designed to sense the magnitudes of theseparameters and react in an appropriate manner to correct the fuel flowaccordingly. However, these mechanisms have not proved to be entirelysatisfactory because of inaccuracies at small force inputs due to theshift in servo operating points, inaccuracies arising from changes infuel temperatures, complicated feed-back cam arrangements, errors due tounbalanced servo hydraulic forces and, lastly, the necessity ofmaintaining a constant operating pressure differential.

It is now proposed to provide a force balance system which will producean output displacement as a function of a force input.

The general object of the invention is to greatly minimize, if notcompletely eliminate the various undesirable conditions previouslymentioned.

More specifically it is an object to provide a force balance systemcomprising pressure responsive means, a lever operable to control thepressure applied to the pressure responsive means, means secured to thepressure responsive means for movement therewith operable to apply aconstant force to the lever at different positions therealong tending tomove the lever in one direction, and means for applying a-force input tothe lever at a fixed location in accordance with the variation of anexternal parameter, whereby movement of the pressure responsive means isproportional to the change of said external parameter.

Still more specifically it is an object of the present invention toprovide a force balance system comprising a piston having at least twoeifective areas and movable within a cylinder, means for applying fluidunder pressure to one of the elfective areas of the piston, valve meansfor reducing the pressure applied to the other effective area of thepiston to cause movement of the piston within the cylinder, a lever forcontrolling the position of the valve, means for applying asubstantially constant force to said lever at different pointstherealong depending on the position of the piston, and means forapplying a force to the lever at a fixed point to cause movement of thelever in a direction to open the valve, which force varies in accordancewith an external parameter.

Another object is to provide a force balance system as set forth abovewherein the means for applying a constant force to the lever comprises aU-shaped spring secured to said piston.

Another object is to provide a force balance system as set forth abovewherein means are provided to compensate for the effect of temperatureon the spring to insure that the spring produces a constantforce on thelever over the operating temperature range of the force balance system.7

Another object is to provide a force balance system which is simple inconstruction, economical to manuf acture and efiicient in use.

Other objects and features of the invention will become apparent as thedescription proceeds, especially when taken in conjunction with theaccompanying drawings, illustrating a preferred embodiment of theinvention, wherein:

FIGURE 1 is a section view of the force balance system of the inventionillustrated in the environment of a fuel control system for a gasturbine power plant.

FIGURE 2 is an illustration of a modification of the force balancesystem shown in FIGURE 1 wherein temperature compensating means areprovided.

FIGURE 3 is an illustration of a portion of the parameter sensing andinput force applying mechanism of the fuel control with which the forcebalance system of the invention is illustrated.

With reference to the figures, a particular embodiment of the presentinvention will now be disclosed.

The force balance system 10, as best shown in FIGURE 1, comprises ahousing 12 which may be a part of a fuel control system for a gasturbine engine (not shown), a piston 14 movable within a cylinder 16formed within the housing 12, a valve 18 for regulating the pressuresapplied to the piston 14, and lever 20 operable to more fully open orclose valve 18. The force balance system 10 further includes springmeans 22 for applying a constant force to lever 20 at various pointstherealong depending upon the position of the piston 14 to which thespring 22 is attached, and sensing means 24 operable to sense an engineparameter and to apply a force variable in accordance with the variationof the engine parameterv opening of valve 18 on an increase of theengine param eter from source 32 as sensed by the sensing means 24 andapplied to lever 20. The piston is therefore caused to move upwardly inFIGURE 1, thus varying the position of the constant force applied to thelever 20 by spring 22 until the lever is returned to the position shownwherein the valve 18 positioned so that pressures P P and P acting onpiston 14 hold the piston in equilibrium.

More specifically the housing 12 which, as indicated above, may be partof a larger fuel control mechanism for a gas turbine engine and includespassages 34, 36 and 38 therein in addition to the cylinder 16 in whichthe piston 14 reciprocates. Also, the housing 12 is provided with aspace therein for the sensing mechanism 24 and includes a cavity or sump40 in which a sink pressure P, is maintained and in which fuel controllevers 42 and 4-4 are mounted for positioning by cam means 46 on axialdisplacement of piston rod 48.

Piston 14, as shown best in FIGURE 1, extends through opening 50 inhousing 12. The piston 14 is formed as shown in FIGURE 1 and is providedwith a centrally located annular flange 52 therearound which operates toguide the piston 14 for movement within the cylinder 16 and furtherdivides the cylinder 16 into a chamber 28 and a chamber 30 wherebypiston 14 is a differential area motion piston.

Valve 18 is secured within housing 12 by convenient means, such asthreads, as shown, and when opened permits passage of fluid betweenchamber 30 and sump 40 through passage 38. Valve 18 is urged toward theopen position by means of spring 54.

' Lever 20 is pivotally mounted in housing 12 by means of pivot pin 56and bearing sleeve 58. Lever 20 is operable to close valve 18 whenrotated in a clockwise direction from the position shown in FIGURE 1 andis rotatable counterclockwise with respect to its position in FIGURE 1to permit opening of valve 13 under influence of spring 54. Lever 20 ispositioned by the spring 22 carried by piston 14 and by the parametersensing means 24 through forces applied thereto tending to causepivoting or the lever 20 about pivot pin 56.

Spring 22 which is generally U-shaped as shown is secured to the end 59of piston 14 by means of pin 60 passing through bracket 62 which is heldin position within the piston 14 by means of bolt 64. Rollers 66 and 68are carried by the opposite ends of spring 22 to permit ready movementof piston 14 and therefore the point of application of the force appliedto the lever 20 by the spring 22 on variation of the pressure inchambers 28 and 39.

The parameter sensing means 24 comprises opposed bellows 70 and 72 whichhave movable adjacent ends and fixed remote ends and a pivotally mountedlever apparatus 74 held between the bellows 70 and 72. Thus on change ofinput parameter, such as compressor inlet pressures P the arm 76 of thelever apparatus 74 is caused to pivot about pivot mounting 78 therefor,whereby the force transmitting arm 80 of lever apparatus 74 is caused totransmit the change in pressure P to the lever 21! at point 82 thereon.

Thus in operation it will be assumed that the pressure P has beenconstant for a period sufiicient to enable the force balance system It}to reach equilibrium with the elements thereof positioned as shown inFIGURE 1. It is then assumed that the pressure P is caused to raise dueto a condition external to the force balance system for which it isdesired to adjust the fuel supply of the gas turbine engine with whichthe force balance system is associated by means of axial adjustment ofthe piston rod 48.

On increase of pressure R; as sensed by the sensing apparatus 24 theforce applied by means of arm 80 of lever apparatus 74 to lever 20 atpoint 82 will also beincreased. The increase of force on lever 20 atpoint 82 will cause lever 20 to rotate counterclockwise whereby valve 18is more fully opened.

More fully opening valve 18 permits increased flow of fluid from chamber30 into sump 20 through passage 38, whereby the pressure P in chamber 30is reduced to a value below pressure P so that the pressure P withinchamber 28 causes movement of piston 14 in an upward direction as shownin FIGURE 1.

Movement of piston 14 in an upward direction changes the location of theapplication of the constant force applied to lever 20 by means of spring22 through roller 68 since spring 22 is mounted for movement with piston14. The piston 14 will be allowed to move to a position such that theforce applied to lever 20 through roller 68 will counteract the forceapplied to lever 20 at point 82 through arm 30 to return the lever .20to the original position thereof.

The valve 18 will then be positioned so that the flow throughrestriction 84 in passage 36 is such that pressure P on piston 14 issuch that it is balanced by the pressures P P and P acting thereon. Thepiston 14 will then again be in equilibrium in a position determined bypressure P Thus it can be seen that due to a rise in pressure R; aproportional movement of the piston rod 48 has beenraccomplished throughmeans of the force balance system whereby the cam 46 is positioned toprovide proper fuel control action through levers 42 and 44 as requiredby the change in pressure P Mathematically it can be seen that if theforce applied at point 82 on lever is indicated by the symbol F and thedistance from the pivot pin 58 to the point of application of force E,is indicated L and the force applied to the lever 20 by means ofspring22 is l and the distance from the pivot pin 58 atwhich it is.applied to the lever 20 is L the forces acting on the lever 20 when thelever is in equilibrium may be represented by the equation:

( 5) s) n) n) From this it is evident that movement of the piston 14will be linear with respect to the force applied to the lever 20 atpoint 82.

FIGURE 2 indicates means for compensating for the effect of temperatureon the spring 22. To provide a linear relationship between the forceapplied to the lever 20 at point 82 and the displacement of the pistonrod 48, it is necessary that the force applied to the lever 20 by meansof spring 22 be constant. Springs, such as 22, however have propertieswhich vary in accordance with the temperature thereof. Therefore, asshown in FIG- URE 2, a compensating spring 86 is sleeved over the pistonrod 48 as shown and is secured to the spring 22 within notches 88therein. Thus with the temperature characteristics of the spring 86properly chosen, the change in characteristics of the spring 22 due totemperature can be compensated for to provide a constant pressure onboth the surface 9% of housing 12 and on the lever 20.

The drawings and the foregoing specification constitute a description ofthe improved force balance system in such full, clear, concise and exactterms as to enable any person skilled in the art to practice theinvention, the scope of which is indicated by the appended claims.

What we claim as our invention is:

1. A force balance system for producing an output movement which variesaccording to the variations of an input parameter, comprising apivotally mounted lever having a control surface, pressure responsivemeans, a U-shaped leaf spring pivoted to said pressure responsive meansat the mid point of said spring whereby said spring is movable withrespect to said lever on movement of said pressure responsive means,rollers secured to both ends of said leaf spring, a fixed surfaceengaging one of said rollers during movement thereof, the other of saidrollers engaging said control surface of said lever during movement ofsaid spring to exert a constant force on said lever at dilferent pointslongitudinally thereof valve means located adjacent and positioned bysaid lever for regulating the pressure applied to the pressureresponsive means and therefore the movement thereof in accordance withthe position of said lever, and means responsive to the variations ofthe input parameter engaged with said lever for urging said lever in theopposite direction.

2. A force balance system for producing an output movement which variesaccording to the variations of an input parameter, comprising apivotally mounted lever having a control surface, pressure responsivemeans, leaf spring means secured to said pressure responsive meansengageable with said control surface of said lever and movabletherealong in response to movement of the pressure responsive meansoperable to exert a constant force on said lever tending to rotate saidlever in one direction, valve means located adjacent and positioned bysaid lever for regulating the pressure applied to the pressureresponsive means and therefore the movement thereof in accordance withthe position of said lever, means responsive to the variations of theinput parameter engaged with said lever for urging said lever in theopposite direction, and means for compensating for the effect oftemperature on said spring to insure the force exerted thereby onsaidlever is constant.

3. A force balance system for producing an output movement which variesaccording to the variations of an input parameter, comprising apivotally mounted lever having a control surface, pressure responsivemeans, leaf spring means secured to said pressure responsive meansengageable with said control surface of said lever and movabletherealong in response to movement of the pressure responsive meansoperable to exert a constant force on said lever tending to rotate saidlever in one direction, valve means located adjacent and positioned bysaid lever for regulating the pressure applied to the pressureresponsive means and therefore the movement thereof in accordance withthe position of said lever, means responsive to the variations of theinput parameter engaged with said lever for urging said lever in theopposite direction, and auxiliary spring means also secured to saidpressure responsive means and operable between said pressure responsivemeans and leaf spring to compensate for the effect of temperature onsaid leaf spring to insure the force exerted thereby on said lever isconstant.

4. A force balance system for producing an output movement which variesaccording to the variations of an input parameter, comprising apivotally mounted lever having a control surface, a two diameter pistonresponsive to changes in pressure, a U-shaped leaf spring pivoted tosaid piston at the mid point of said spring whereby said spring ismovable with respect to said lever on movement of said piston, rollerssecured to both ends of said leaf spring, a fixed surface engaging oneof said rollers during movement thereof the other of said rollersengaging said control surface of said lever during movement of saidspring to exert a constant force on said lever at diflerent pointslongitudinally thereof, valve means located adjacent and positioned bysaid lever for regulating the pressure applied to the piston andtherefore the movement thereof in accordance with the position of saidlever, and means engaged with said lever responsive to the variations ofthe input parameter for urging said lever in the opposite direction.

5. A force balance system for producing an output movement which variesaccording to the variations of an input parameter, comprising apivotally mounted lever having a control surface, a two diameter pistonresponsive to changes in pressure, a U-shaped leaf spring pivoted tosaid piston at the mid point of said spring whereby said spring ismovable with respect to said lever on movement of said piston, rollerssecured to both ends of said leaf spring, a fixed surface engaging oneof said rollers during movement thereof, the other of said rollersengaging said control surface of said lever during movement of saidspring to exert a constant force on said lever at different pointslongitudinally thereof, valve means located adjacent and positioned bysaid lever for regulating the pressure applied to the piston andtherefore the movement thereof in accordance with the position of saidlever,

eans engaged with said lever responsive to the variations of the inputparameter for urging said lever in the opposite direction, and auxiliaryspring means also secured to said pressure responsive means and operablebetween said pressure responsive means and leaf spring to compensate forthe efiect of temperature on said leaf spring to insure the forceexerted thereby on said lever is constant.

6. A closed loop moment balance system for sensing an engine operatingparameter, said system comprising a multi-diameter piston adapted to beinfluenced by at least two distinct fluid pressures, a pivotallysupported moment arm, leaf-type spring means adapted to create a forceconnected to said piston in a manner so as to be capable of applyingsaid created force at various points along said moment arm, thermostaticmeans cooperating with said leaf-type spring means adapted to compensatefor variations in said created force due to temperature changes, valvemeans secured to the free end of said moment arm for varying themagnitude of one of said distinct fluid pressures, and means fordirecting a force input to said moment arm for actuating said valvemeans.

7. A mechanical computing device for creating an output movementproportional to the magnitude of a force input, said device comprising apiston responsive to changes in pressure, a leaf spring secured to saidpiston, a plurality of rollers cooperating with and being normally urgedaway from each other by said leaf spring secured to said piston, arestraining member positively limiting the outward movement of one ofsaid rollers, a pivotally mounted second restraining member yieldinglylimiting the outward movement of the other of said rollers, a servovalve connected to said second restraining member for varying themagnitude of one of the various pressures influencing said piston, andmeans for directing said force input to said second restraining memberat a distance away from the pivoted mounting thereof.

8. A closed loop moment balance system for sensing an engine operatingparameter, said system comprising a multi-diameter piston adapted to beinfluenced by at least two distinct fluid pressures, a pivotallysupported moment arm, leaf-type spring means adapted to create a forceconnected to said piston in a manner so as to be capable of applyingsaid created force at various points along said moment arm, auxiliaryspring means alsoconnected to said piston and operable between thepiston and leaf spring to compensate for the effect of temperature onthe leaf spring to insure the force exerted by the leaf spring on themoment arm is constant, valve means secured to the free end of saidmoment arm for varying the magnitude of one of said distinct fluidpressures, and means for directing a force input to said moment arm foractuating said valve means.

9. A mechanical computing device for creating an output movementproportional to the magnitude of a force input, said device comprising apiston responsive to changes in pressure, a leaf spring secured to=saidpiston, a plurality of rollers cooperating with and being normally urgedaway from each other by said leaf spring secured to said piston, arestraining member positively limiting the outward movement of one ofsaid rollers, a pivotally mounted second restraining member yieldinglylimiting the outward movement of the other of said rollers, a servovalve connected to said second restraining member for varying themagnitude of one of the various pres-sures influencing said piston,means for directing said force input to said second restraining memberat a distance away from the pivoted mounting thereof, and means forcompensating for the effect of temperature on said spring to insure theforce exerted thereby on said second restraining member is constant.

l(). A force balance system for producing an output movement whichvaries according to the variations of an input parameter, comprising apivotally mounted lever having a control surface, pressure responsivemeans, a U-shaped leaf spring pivoted to said pressure responsive meansat the mid point of said spring whereby said spring is movable withrespect tosaid lever on movement of said pressure responsive means,rollers secured to both ends of said leaf spring, a fixed surfaceengaging one of said rollers during movement thereof, the other of saidrollers engaging said control surface of said lever during movement ofsaid spring to exert a constant force on said lever at different pointslongitudinally thereof, valve means located adjacent and positioned bysaid lever for regulating the pressure applied to the pressureresponsive means and therefore the movement thereof in accordance withthe position of said lever, means responsive to the variations of theinput parameter engaged with said lever for urging said lever in theopposite direction, and means for compensating for the effect oftemperature on said spring to insure the force exerted thereby on saidlever is constant.

11. A force balance system for producing an output movement which variesaccording to the variations of an input parameter, comprising apivotally mounted lever having a control surface, pressure responsivemeans, a U-shaped leaf spring pivoted to said pressure responsive meansat the mid point of said spring whereby said spring is movable withrespect to said lever on movement of said pressure responsive means,rollers secured to both ends of said leaf spring, a fixed surfaceengaging one of said rollers during movement thereof, the other of saidrollers engaging said control surface of said lever during movement ofsaid spring to exert a constant force on said lever at difierent pointslongitudinally thereof, valve means located adjacent and positioned bysaid lever for regulating the pressure applied to the pressureresponsive means and therefore the: movement thereof in accordance withthe position of said lever, means responsive to the variations of theinput parameter engaged with said lever for urging said lever in theopposite direction, and auxiliary spring means also secured to saidpressure responsive means and operable between said pressure responsivemeans and leaf spring to compensate for the effect of temperature onsaid leaf spring to insure the force exerted thereby on said lever isconstant.

12. A force balance system for producing an output movement which variesaccording to the variations of an input parameter, comprising apivotally mounted lever having a control surface, a two diameter pistonresponsive to changes in pressure, a U-shaped leaf spring pivoted tosaid piston at the mid point of said spring whereby said spring ismovable With respect to said lever on movement of said piston, rollerssecured to both ends of said leaf spring, a fixed surface engaging oneof said rollers during movement thereof, the other of said rollersengaging said control surface of said lever during movement of saidspring to exert a constant force on said lever at different pointslongitudinally thereof, valve means located adjacent and positioned bysaid lever for regulating the pressure applied to the piston andtherefore the movement thereof in accordance with the position of saidlever, means engaged with said lever responsive to the variations of theinput parameter for urging said lever in the opposite direction, andmeans for compensating for the effect of temperature on said spring toinsure the force exerted thereby on said lever is constant.

References Cited in the file of this patent UNITED STATES PATENTS1,798,932 Dreiske Mar. 31, 1931 2,220,180 Spitzglass et al. Nov. 5, 19402,600,777 Johnson June 17, 1952 2,764,868 Watson et a1. Oct. 2, 1956FOREIGN PATENTS 734,621 Great Britain Aug. 3, 1955

